Using double labelling techniques the rate of incorporation of proline into rat liver collagen has been studied in rats receiving a cirrhogenic diet over a period of 21 weeks. From the specific activity of the injected proline, and the calculated size of the proline pool, as well as by an experimental design allowing the sacrifice of rats at different intervals after injection, the effect of ethanol on the rates of synthesis and of degradation of hepatic collagen will be determined. Ethanol appears to inhibit the degradation of collagen suggestion that the mechanism may involve inhibition by ethanol of lysolomal acid hydrolases. Experiments to test this proposition are in progress.